Dear David, and R-users,

thanks for the response. I'll do my best to describe the context.

My data consists in two matrices, D and T. The former provides simple 
values, the latter is a Boolean matrix. The number of rows in D is equal 
to the number of columns in T.

My aim is to construct a larger matrix which is made up of sum(T) 
diagonal matrices constructed from the rows of D, and placed according 
to a structure given by a transformation of T.

Whereas the positions of the columns in which T is equal to 1 informs 
about the placement of the diagonal matrices, the positions of the rows 
in which T is equal to 1 informs about which row to take from D in order 
to create these diagonal matrices.
In the code below (corrected in the last line with respect to the 
previous version, sorry), I first created the matrices D and T. Then I 
built a 0/1 matrix (M0) that presents the structure of the final 
block-matrix made up of diagonal matrices, and, by Kronecker product, a 
matrix with the final 0/1 structure is constructed, M.
Using the rows in which T is equal to 1, I select the values from D and 
place in the matrix M, where such matrix is equal to 1.

It's a long explanation and I could not find a better way to program 
(and explain) it.

Thanks for you help,
Giancarlo


## data in matrices
D <- matrix(1:15, 3, 5)
T <- matrix(0, 3, 3)
T[c(2,4,6,8)] <- 1

## the col of T equal to 1 gives the position
wr <- which(T==1, arr.ind=TRUE)[,2]
## we aim to sum(T) diagonal matrices
wc <- 1:sum(T)
## structure: how to place the diagonal matrices
M0 <- matrix(0, nrow(T), sum(T))
M0[cbind(wr,wc)] <- 1

## number of columns
m <- ncol(D)
## final 0/1 matrix
M <- kronecker(M0, diag(m))

## the row of T equal to 1 gives which rows to take from D
pos <- which(T==1, arr.ind=TRUE)[,1]
## filling up with data
M[M!=0] <- t(D[pos,])


On 29/01/2014 01:49, David Winsemius wrote:
> On Jan 27, 2014, at 8:04 AM, Carlo Giovanni Camarda wrote:
>
>> Dear R-users,
>>
>> I would like to know whether you know some trick for skipping some of
>> the steps in the example below (especially the last step in a way that
>> would make easier to be written succinctly in a text).
>>
>> I could try to explain in words the whole process, but I'm sure the code
>> below would be clearer.
> After looking at the code and output, I must disagree. The lack of any response from the rest of the readership suggests to me that I am not the only one who thinks a natural language description of the context and goals for this effort would help.
>
>> Thanks in advance for your help,
>> Giancarlo
>>
>>
>> ## data in matrices
>> D <- matrix(1:15, 3, 5)
>> T <- matrix(0, 3, 3)
>> T[c(2,4,6,8)] <- 1
>>
>> ## how to place the diag matrices of each row
>> M0 <- matrix(0, nrow(T), sum(T))
>> wr <- which(T==1, arr.ind=TRUE)[,2]
>> wc <- 1:ncol(M0)
>> M0[cbind(wr,wc)] <- 1
>>
>> ## number of columns
>> m <- ncol(D)
>> ## non-zero positions
>> M <- kronecker(M0, diag(m))
>> ## which rows to take
>> pos <- which(T==1, arr.ind=TRUE)[,1]
>> ## filling up with data
>> M[M!=0] <- t(D[wr,])
>>
>> 	[[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> David Winsemius
> Alameda, CA, USA
>


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